Hydrogen is a representative clean energy, and it is no doubt that an inexpensive method for producing it will increasingly be required in the market. Currently, a major hydrogen producing method is a method in which a methane gas as a main ingredient of a natural gas is brought into contact with a steam at 700 to 800° C. whereby allowing it to be reformed into a hydrogen (steam reforming method). Nevertheless, this steam reforming method allows about 10 to 20% of the methane gas to remain as being unreformed, although it allows for a methane gas-to-hydrogen reforming rate as high as 80% or more. Accordingly, various attempts have been made in studies to reform the unreformed remaining methane gas to hydrogen by utilizing the residual heat of this steam reforming method. For example, Lodeng et. al. studied a catalytic method in which an alumina particle is allowed to carry a metal microparticle exerting a catalytic performance for reforming the methane gas such as a cobalt, nickel and iron, and the results of the study was published in 2007 (Non-Patent literature 1). However, the cobalt poses a problem due to its water solubility and the nickel and the iron suffer from a reduced catalytic performance due to a promoted oxidation, since a natural gas whose main ingredient is a methane gas which is gushed out of the underground actually contains, in addition to the steam, an erosive gas such as a hydrogen sulfide. Accordingly, when utilizing the nickel and the iron as reforming catalyst metals, every utilization requires a heating at several hundreds° C. while supplying hydrogen to reduce the oxidized nickel oxide and iron oxide for re-metallization, which poses a substantial problem with regard to the cost. Therefore, when considering an actual natural gas as a resource for the hydrogen gas production, it is a practical and critical problem how an extremely low-oxidizable noble metal catalyst such as a platinum and a palladium can be used at a low cost while maintaining the methane gas reforming performance. Moreover, a substance employed as a carrier for a noble metal catalyst microparticle is responsible not only for just carrying the noble metal catalyst microparticle. For example, when using an alumina as a carrier, the stability is ensured chemically and crystallographycally even at a temperature as high as 700° C., but a toxic carbon monoxide is produced as a by-product when reforming a methane gas to produce a hydrogen gas. Also when using as a carrier a carbon material such as an activated carbon, the carbon itself undergoes calcination with no resistance against a temperature of several hundred° C. if oxygen is mixed in the methane gas.
In view of the background described above, a technology enabling a hydrogen production by allowing a catalyst microparticle of a palladium, which is least expensive among the noble metals employed effectively in obtaining hydrogen by reforming a methane gas, to be carried on a carrier material which is heat resistant and does not produce carbon monoxide as a by-product is highly demanded. Accordingly, we proposed that a palladium catalyst microparticle is deposited chemically on the surface of a manganese dioxide having a ramsdellite-type crystal structure and used as a reformed catalyst (Patent Literature 1).